#include <iostream>
#include <iomanip>
using namespace std;

int fibonacci(int i);

int fibonacci(int i) {
    if (i == 1 || i == 2)
    {
        return 1;
    }
    else
    {
        return fibonacci(i - 1) + fibonacci(i - 2);
    }
}

int main()
{
    cout << setprecision(2) << fixed;
    int num_count;
    cin >> num_count;
    double sum = 0;
    for (int i = 1; i <= num_count; i++)
    {
        sum += (double)(fibonacci(i + 2) / (double)fibonacci(i + 1));
    }

    cout << sum << endl;
    return 0;
}